An oil gun and a caulk gun are known as a toll for s dispensing a viscosity fluid. The oil gun is used for changing a differential oil or transmission oil upon a maintenance of automobiles. Standard type oil gun has a cylinder and a piston rod. The oil gun of the type requires a strong power for pushing and drawing the piston rod in order to dispense and suck a high viscosity oil.
Caulk guns are used for coating and injecting a sealing material on construction sites. A caulk gun, described in U.S. Pat. No. 2,768,768, has a cylinder and a piston rod provided with a reversible ratchet mechanism. The ratchet mechanism is for switching the moving direction of the piston rod in the forward direction or the backward direction. This mechanism is also provided with teeth formed on the piston rod and pawls activated by a lever. When the ratchet mechanism is switched such that the piston rod dose not move in one direction and then the lever is activated, the piston rod is allowed to be moved in the other direction. However, the purpose of the caulk gun, described in the patent, is for eliminating occurrence of afterflow following gun operation (shown in C.1, Lines 59 to 60.) Furthermore, the caulk gun needs a process to slide a sleeve in order to switch the moving direction of the piston rod.